Most fully automatic rifles are illegal to own, except for under a few circumstances, so gun accessory manufacturers got creative. They found a way to use a rifle’s natural firing physics as a method for increasing its bullet output. Enter the “bump stock,” or “bump fire stock.” They’re after-market gun modifications that utilize a semi-automatic rifle’s recoil to bounce its stock back and forth off of the shooter’s shoulder and re-cock the gun after each round fired. While firing, the shooter has to hold their trigger finger in place while simultaneously pushing the barrel forward and pulling the pistol grip backward as it “bumps.”

Basically, it lets you pull the trigger once and empty an entire clip lickity split. Suddenly, a semi-automatic rifle—which can normally only fire one bullet per trigger pull—fires in a way that’s similar to a fully automatic rifle. The video below from No Surrender Productions shows how one of the more popular brands of bump stocks, Slide Fire, works:

Semi-auto fire at 0:43 and bump stock fire at 1:22.

These devices are 100% legal (a semi-automatic rifle equipped with one is still not classified as an automatic weapon), and to use them all you have to do is replace your rifle’s standard stock with the bump stock. Combine one of these with a 100-round magazine and you’ve essentially got a full-fledged machine gun in your hands.

These accessories are technically legal loopholes for providing simulated automatic fire without breaking any laws. But the legality of these devices may change soon. On Wednesday, top Republicans in congress said they’d be open to banning them. And Texas Senator John Cornyn expressed his distaste for the modifications in question:

“I own a lot of guns, and as a hunter and sportsman, I think that’s our right as Americans, but I don’t understand the use of this bump stock. It seems like it’s an obvious area we ought to explore and see if it’s something Congress needs to act on.”

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Other lawmakers seem to be on board with reviewing these devices, so it could just be a matter of time before they’re gone for good. Even the Slide Fire home page says at the very top that they’ve “...decided to temporarily suspend taking new orders in order to provide the best service with those already placed.” Perhaps the end of the bump stock is nigh and some gun reform is on the way.